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AP®︎/College Biology
Taxonomy and the tree of life
Carl Linnaeus, the father of modern taxonomy, developed a system for classifying living organisms into categories like species, genus, order, class, and kingdom. This tree of life helps us understand relationships between organisms. Taxonomy is both an art and a science, with DNA analysis now playing a significant role. Humans are also classified within this system, highlighting our connections to other life forms. Created by Sal Khan.
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- Are races human subspecies?(32 votes)
- You can think about it that way if you find it helpful, but races are not generally considered subspecies. Most people tend to think of subspecies as populations capable of interbreeding (hence, still the same species) but prevented from doing so by some other mechanism such as geographical or behavioral isolation. It is further generally assumed that subspecies are more distinct from one another than are races or breeds.
Really, from a biological perspective, there's very little difference between races of humans. Based on ancestry and geographical distribution, certain patterns do emerge, but the genetic differences between individuals of the same race can be just as great as the genetic differences between individuals of different races.(83 votes)
- Why did Linneas also include minerals as a third kingdom?(22 votes)
- His taxonomy of minerals has dropped long since from use. In the tenth edition, 1758, of the Systema Naturæ, the Linnaean classes were:
Classis 1. Petræ
Classis 2. Mineræ
Classis 3. Fossilia
Classis 4. Vitamentra
Hope that helped!
http://en.wikipedia.org/wiki/Linnaean_taxonomy#For_minerals(16 votes)
- I thought there were only 7 categories: Kingdom, Phylum, Class, Order, Family, Genus, Species.
Is Domain one of them, or is it just a name for everything? I am really confused here.(9 votes)- A domain is a group above kingdom. There are three domains which are then divided into the 6 kindgoms.(12 votes)
- okay . but i am still not clear about the difference between genus and species(3 votes)
- A 'Species' is a population, or group of populations of individuals of the same species, of whose members have the potential to interbreed with each other, and produce fertile offspring, and 'Genus' is a group to which a 'species' belongs. A classic (i.e textbook :P) example is the Leopard. The Leopard is the 'Species', and the species Leopard belongs to the 'Genus' Panthera, so large cats (e.g. Lions, Tigers, etc).(12 votes)
- As I know very little about the tree of life, its not my field. However I did this video very interesting. My question, my son watched the video with me and told me that dogs and horses are related. He is in the 6th grade. How would this be listed if it were true. Mammals, Four legs, Fur, but how else?(2 votes)
- The tree of life is a metaphor for the fact that all life on earth is evolutionarily related, somewhat like a huge version of a human family tree. The tree really has nothing to do with physical characteristics such as fur or number of legs. Because evolution allows lineages to change physiologically and anatomically, many pairs of species on earth are quite different.
When we look at two species whose members outwardly appear somewhat similar, this is a clue that they share a recent common ancestor. For example, dogs and horses are biologically separate lineages, however they are similar enough (four legs, fur) that it is highly likely that the two lineages split more recently, such as two first cousins who's most recent common ancestor was a grandparent. When we talk about a biological common ancestor, we really mean an ancestral species consisting of many individuals. A "grandparent population" that split and became two separate populations, which persisted into becoming modern day dogs and horses.
On the other hand, dogs and mosquitoes are very different, which is a clue that their common ancestor diverged into the two lineages a very long time ago, like two distant cousins sharing a great great great great great great grandparent. This ancestral species probably outwardly looked nothing like either a dog or a mosquito.
So the whole idea of the tree of life is to convey the idea that all living species, including dogs, horses, and mosquitoes are related, even though some are more closely related than others.(7 votes)
- At around, Sal mentioned that till this day, people are still debating whether this method is the best way to classify organisms. So may I know what is the other method(s)? Thanks. 2:58(3 votes)
- A long time ago everything was classified as either an animal or a plant. This was before they knew about microscopic life. Once this was known most biologists adopted the 5 kingdom system which I was taught in 6th grade and which some people still cling to.
The Tree of Life is the most accurate representation of true evolutionary relationships out of any other system, but there is still room for other useful systems. For example, a doctor might not need to know the evolutionary relationships of all bacteria, since the vast majority of them are not harmful, only certain more or less randomly scattered strains on the tree. He might instead want to classify them into groups based on how dangerous they are to human health.(2 votes)
- When you were talking about the humans are you trying to say we evolved from monkeys(3 votes)
- Kind of, not the modern monkeys you see today though. Humans and all monkeys share a common ancestor through which all of them evolved from (this ancestor would probably look similar to a monkey). The beings that would become humans evolved from that into a new species that would be the common ancestor to all apes that we know of. Evolution is not a straight road, it is like a tree, all the end pieces of branches are the creatures that we see today and the parts where branches join are where the common ancestors are.(5 votes)
- What does DNA mean ?? does it have a full form ?(2 votes)
- DNA is an acronym for deoxyribonucleic acid. It's kind of like an instruction book on how to build an organism, also dictating cell structure and function.(5 votes)
- are races humans subspecies(2 votes)
- No, race is an arbitrary distinction that is meaningless from a biological perspective.(5 votes)
- Does "taxonomy" have a Greek or Latin derived root?(2 votes)
- yes. it has a root from the greek language. "taxis" means arrangement and "nomia" means method.(5 votes)
Video transcript
This right here is a
picture of Carl Linnaeus, and I'm sure I'm
mispronouncing the word. He's a Swedish gentleman
who lived in the 1700s, and he's known as the
father of modern taxonomy. And the word
taxonomy, if you just split up into its
original root, it really is the science of really
classifying things. But when people talk about
taxonomy-- and in particular, in Carl Linnaeus'
case-- they're talking about the
classification of living things, so
classifying organisms. And his real innovation--
before he came about, peopled realize that you had
species of animals, that lions had certain
properties that made them all lions, that
they could interbreed and things like that, that
monkey or chimpanzees would all interbreed and that would
be a separate species and that polar bears
were separate species and that humans were
a separate species. But what he really brought
to the table was he decided, well, let me not just
group animals into species. Maybe I can group species
into other categories. And that's where we
get the genus from. You group similar
species into a genus. And then he went
even beyond that, because even the idea
of grouping things into a genus dated back
to the ancient Greeks. He said, well, why don't I
group similar genuses together into orders, orders together
into classes, and then classes together into kingdoms. So really what he
did is he said, well, maybe I can classify--
I can create a tree. I can create a tree of life. I can create a structure
so we can really see how far apart any
two organisms are, and so that's why
he's really the father about modern taxonomy. And he did not have many tools. All he could do was look at
his powers of observations and say, OK, those kind
of animals, they have fur, or they reproduce in this way. Or they lay eggs, or
they don't lay eggs. Or they have spinal columns, or
they don't have spinal columns. So that's the best that he could
do when he did his taxonomy. But since then,
there's obviously been tons of innovations
in how we perceive animals, or the natural world,
and our tools for studying them. So one thing that he
did not know about is evolution-- this
idea of common ancestry. And between our
understandings of evolution and our ability to look
back at the fossil record, that helps us get more
precise at figuring out which animals are
related to which. We can see, do they have a
common ancestor more recent or further back. And what even Charles
Darwin didn't have, which we now use as
a tool in taxonomy, is the genetic evidence. So now we don't even have to
rely on the fossil record. We could look at the DNA of
two species that exist today and see how similar is that DNA. And that tells us how
recently they branched apart if we were able to find
it in the fossil record or how recently in the past
did these two species become two different species. Now, with that said, I do
want to make this clear. And this is something
that I've always had a little bit-- it was fuzzy
for me the first time that I was exposed to this
idea of taxonomy-- is that taxonomy is as much
an art as it's a science. And today, even to
this day, people are debating about the
best way to classify things and what do you
pay attention to. And DNA has been
the best tool so far in giving us a more systematic,
a more analytical way, of deciding how close
two animals are. But to a large degree, a lot
of these categories-- deciding where to divide along kingdom,
phylum, class, order, family, tribe-- these are
somewhat arbitrary. These are just picked based on
early taxonomists, including Carl Linnaeus, and
saying, well, this looks like a grouping
right over here. But they could have grouped
at a broader level or a deeper level. So these things right over
here are somewhat arbitrary. A more analytical way is
just to see how much DNA you have in common and then use that
as a measure of how far apart two animals are. Or really, I should
say, two species are, because this taxonomy doesn't
only apply just to animals. It applies to plants
and bacteria and Archaea and all sorts of
things, so it's actually a broader thing
than just animals. Now, with that out of
the way, what I thought would be fun-- just so
that we could really get a sense of where
modern taxonomy is, where the field that was essentially
fathered by Carl Linnaeus, where it is now, how we-- and
use that to figure out where we humans fit into the big picture. And obviously, I'm drawing
just a small fraction of the universe of the
organisms that we even know about right now. But at least it frames the
picture in terms of something we understand--
in particular, us. In particular, humans. Now, our species, we
call ourselves humans. But we're really Homo sapiens. And the sapiens is
the species part, and then Homo is the genus. And what I'm doing
right over here is I'm saying, well, if
Homo is the genus, what other species were
inside of Homo? And the reality is--
or at least as far as we know-- there are no other
living species inside of Homo. We probably killed them all off. Or maybe we interbreeded
with them somehow, which might have
argued that maybe they weren't different species. But more likely,
they were competing in the same ecosystems, and
they became endangered species very quickly when they
competed with our ancestors. But the most recent
other species within the genus that we know
about are the neanderthals, and the formal term for their
species is neanderthalensis. Now, if we go further
up the tree of life, further up the taxonomy--
and you'll sometimes see tribe mentioned. Sometimes you won't. And we tend to get a
little bit more granular the closer we get to humans. When we go further away
in the tree of life, we get a little bit
less granular sometimes. But that's not always
the case as well. You go a little bit further
up, then you get Hominini. And I'm sure I'm mispronouncing
some of this as well. But another species that's in
Homonini that is not in Homo-- and I'm definitely not
listing all of them, and that's why I'm showing
all of these other branches over here-- is what we
call the common chimpanzee. And their species name
is-- their genus is Pan, and their species
is troglodytes. So you would refer to
them as Pan troglodytes. And that's also
another convention that Carl Linnaeus
came up with, is that you refer to a
particular species by its genus and
then its species. And you capitalize the genus,
and you lowercase a species. So we're Homo sapiens. This is Homo neanderthalensis. This Pan troglodytes or often
referred to as chimpanzees. Now, if you go up one
higher level of broadness on this tree of life, you
then get to the family. And we are in the
family Hominidae, and I'm sure I'm
mispronouncing it once again. But just to give you an
example, so everything I've listed so far, everything
I've talked about so far are within this family. And to show you an animal
that is not in this family, you just have to
look at the gorilla. And you could call it
the Gorillini gorilla, or G gorilla. That's its actual species name. And this family right over
here, sometimes the common term is the great apes. Now, you go one further
level-- and the whole reason why I'm doing this--
and I'm not by any means being exhaustive about
the other species that are in that family, but
that are not in our tribe. I'm just trying to give
you a picture of-- as we get further and further
out, as we get further out of our tribe, our
family, our order, we're getting to things where
the common ancestry with human goes further and
further back in time. The genetic similarities
become more and more different. And even just the
physical differences, if we look it at a very
superficial level, become more and more and
more different. So you get to even
a broader category. This is where you
get to the primates, and this is probably
something that you might be somewhat familiar with. And the term
primates is generally these animals that
look like they either live in trees or a
rain forest, or they're a descendant of things
that live in trees. So they have these things that
they can grasp things with. They're good at
climbing, broadly. Not all of them are. Humans are probably
the worst primates when it comes to climbing,
or one of the worst. But that's the general
classification. That's what we generally think
of when we think of primates. And if we think of a primate
that is not a great ape, you just have to
think of a baboon. So this right here is a baboon. It is a primate, but
it is not a great ape. It is probably a descendant--
some baboons actually don't live in trees. But all of them are
probably a descendant from things that
first lived in trees, and that's why their
hands and their feet look the way they do. Now you get to even a broader
level of classification. You get to the mammals. And once again,
probably something you're used to thinking about. Mammals are
air-breathing animals, and they tend to
have fur or hair. They tend to provide some
form of milk for their young. They have active mammary glands. There's other things we can
talk about, what makes a mammal. I'm not going to go into
the rigorous definition. But just to give you an
example of a mammal that is not a primate, I could show you
this polar bear right over here. This is a mammal that
is not a primate. And I could do other things. I could show you a
tiger, or I could show you a giraffe or a horse. And so by no stretch
of the imagination am I being comprehensive. But let's keep getting broader. Now let's go to the
class-- we're already at the class of Mammalia. Now let's go to the phylum. In phylum, we are--
humans and all mammals, we are in the phylum chordates. And chordates, we're
actually in the subphylum, which I didn't write
here, vertebrates, which means we have a vertebra. We have a spinal column
with a spinal cord in it. Chordates are a little
bit more general. Chordates is a
phylum where-- kind of the arrangement of
where the mouth is, where are the digestive organs,
where the anus is, where the spinal column
is, where are the brains, where are the eyes,
where are the mouth. They're kind of all
in the same place. And if you think
about it, everything I've listed here kind of has
the same general structure. You have a spinal column. You have a brain. You have a mouth. Then the mouth leads to
some type digestive column. And at the end of it, you
have an anus over there. And you have eyes in
front of the brain. And so this is a general way--
and I'm not being very rigorous here, is how you
describe a chordate. And to show a chordate
that is not a mammal, you would just have to
think of a fish or sharks. So this right over here
is a non-mammal chordate This is a great white
shark over here. Now, let's go even broader. As you'll see, now
we're going to things that are very, very
not human-like. So you go one step broader. Now we're in Animalia,
the kingdom of animals. And this is the
broadest category that Carl Linnaeus
thought about. Well actually, he did
go into trees as well. But when you think
of kingdom animals and you think of things
that aren't chordates, you start going into
things like insects. And you start going into
things like jellyfish. If you go even broader, now
we're talking about the domain. You go to Eukarya. So these are all
organisms that have cells. And inside those cells, they
have complex structures. So if you're a Eukarya, you have
cells with complex structures. If you're a Prokarya, you
don't have complex structures inside your cell. But other Eukarya
that are not animals include things like plants. And obviously, I'm
giving no justice to this whole branch
of the tree of life. It could be just as rich
or richer than everything I've drawn over here. This is just a small fraction
of the entire tree of life, but let's go even
broader than that. So if you go even
broader than that, you say, well, what's
a kind of life form that isn't Eukarya, that
wouldn't have these more complex cell structures, the
mitochondria in the cells, the cell nucleuses? Then you just have to think
about something like bacteria. And if you want to
go even broader, there's things like
viruses that you could even debate whether they
really even are life, because they are
dependent on other life forms for their
actual reproduction. But they do have genetic
material, like everything else. And that, to me, is kind
of a mind-blowing idea. As different as
a plant is-- look at a house plant that is
in your house right now or the tree when you walk home
or bacteria or this jellyfish. There is a commonality
in that we all have DNA. And that DNA, for the
most part, replicates in a very, very,
very, similar way. So it's actually crazy that
we actually even are related or that we even do have a
common ancestor with some of these things. And then it even begs
the question, well, what about things like viruses? Anyway, I'll leave you here. And I really just
want to let you know that-- make sure you
realize that this is a-- it's definitely worth studying,
because we understand where we fit in in the universe
of living things. But I also want to
let you know that it is a little bit of an
art on where you decide where to make these
classifications or where you decide to
focus on, whether you want to focus on
what properties, whether it's how they reproduce
or how they feed their young or can they move around
or what they breathe or whatever, things like that. Anyway, I'll let you go there.